Laser robot with heat eliminating means

ABSTRACT

A heat eliminator intercepts a heat transmission in a laser robot which has a robot base (12), a robot arm (16) joined for swing motion to a robot swivel post (14) set upright on the robot base (12), a laser beam projecting unit (20) attached to an extreme end of the robot arm (16), and a drive motor (Mv) for driving the robot arm (16) for a swing motion through a precision transmission mechanism (30, 32, 34) inserted between the robot swivel post and the robot arm, from the drive motor to the precision transmission mechanism. The heat eliminator is provided with a bracket member (26) arranged between the precision transmission mechanism (30, 32, 34) and the drive motor (Mv) with one end in contact with the end surface of the drive motor on the side of the output shaft thereof and the other end in contact with the precision transmission mechanism, and an annular cooling water passage (50) formed in the bracket member (26). Cooling water is supplied into the annular cooling water passage (50) formed in the bracket member (26) from a cooling water source (70) for supplying cooling water to the laser beam conduit lines of the robot arm (16) to cool the bracket member (26) to absorb heat generated by the drive motor (Mv) by the bracket member (26), so that the heat transmission to the precision transmission mechanism (30, 32, 34) is intercepted.

TECHNICAL FIELD

The present invention relates to a laser robot, and more particularly,to a laser robot provided with a heat eliminating means for forciblyremoving heat generated by a drive motor for driving a robot armprovided with a laser beam projecting unit at an extremity thereof, byusing a cooling water supplied from a cooling water supply source tocool a laser beam piping system to thereby intercept a heat transferfrom the drive motor to a precision transmission mechanism includingball screw mechanisms interposed between the drive motor and the robotarm, so that an error in the transmission of a motion due to the thermaldeformation of the precision transmission mechanism is prevented and therobot arm is permitted to operate at a high accuracy, to therebyeventually enable the laser beam projecting unit to accurately determinea projecting direction of the laser beam to a desired position.

BACKGROUND ART

Laser robots of various types have been proposed, and an articulatedindustrial laser robot is disclosed in the pending International PatentApplication PCT/JP90/00104 of the same Applicant as the presentapplication. This laser robot obtains a laser beam emitted by a laserbeam oscillator and led by conduit lines to the robot unit, and leadsthe laser beam through laser beam conduit lines arranged to run in therobot unit and an optical system for deflecting the laser beam to alaser beam projecting unit joined to an extremity of the robot arm ofthe robot unit toward a desired position. The robot unit of the laserrobot comprises a plurality of movable components, such as a swivelpost, robot arms and a robot wrist, and these movable components arecontrolled to direct the laser beam projecting unit toward the desiredposition. Accordingly, many drive motors, especially electric motors,are employed for driving those movable components of the robot unit forcausing a turning, a swinging, and/or a telescopic motion thereof.

Nevertheless, since these drive motors actuate the movable componentsthrough mechanical transmission mechanisms, a thermal deformation of therespective mechanical transmission mechanisms caused by heat, i.e.,Joule heat when the drive motors are electric motors, generated by thedrive motors generates an error in the motion of the respective movablecomponents.

Particularly, a swing mechanism disposed between the electric motor andthe robot arm to drive the robot arm for an up-and-down swing motionabout a horizontal axis in a vertical plane includes a precisionball-screw mechanism and a linkage, i.e., a mechanism comprising aball-screw driven for rotation by an electric motor, and a ball-nutengaged with the ball screw and capable of transmitting a linear motionthereof through the linkage to the robot arm, to thereby swing the robotarm about a horizontal axis. Although the precision ball-screw mechanismhas only a small amount of backlash, to be thus able to exhibit a highaccuracy when controlling the robot arm, the axial length of theball-screw is often changed when the ball screw mechanism is exposed toheat generated by the electric motor. Accordingly, the control of robotmotions is made unstable by the heat generated during a transient periodbefore the temperature of the ball-screw and the associated partsincreased by the heat generated by the electric motor reaches a thermalequilibrium condition, after an electric power source connected to therobot unit is has been turned on to start the robot unit. This longtransient period, however, significantly reduces the rate of operationof the laser robot.

To solve the problem attributable to the heat generated by the electricmotor, another laser robot has been provided wherein a cooling fan isemployed to provide forced cooling of the electric motor. Nevertheless,a cooling of the entire electric motor requires a cooling fan having alarge cooling capacity, which increases the size of the cooling fan andunavoidably entails an increase in the manufacturing cost of the robotunit, in addition to inclusion of the fan per se.

DISCLOSURE OF THE INVENTION

Accordingly, an object of the present invention is to solve theafore-mentioned problem encountered by the conventional laser robots.

Another object of the present invention is to provide a laser robotprovided with a heat eliminating means capable of removing heatgenerated by an electric drive motor, and of being simply incorporatedinto an existing laser robot to thus improve same.

A further object of the present invention is to provide a heateliminating means having a compact construction suitable for a laserrobot, capable of being manufactured at a low cost, and of beingaccommodated in the laser robot, without an increase in size of thelaser robot.

In view of the foregoing objects, in accordance with the presentinvention, there is provided a laser robot which comprises: a robotbase, a robot swivel post arranged upright on the robot base to beturnable about a vertical axis; an axially extendable robot arm jointedto the robot swivel post to be swingable up and down in a vertical planerelative to the robot swivel post and provided with laser beam conduitlines formed therein to lead a laser beam toward an extreme end thereof;a laser beam projecting unit attached to the extreme end of the robotarm for projecting the laser beam led thereto; a drive motor for drivinga swing motion of the robot arm via a precision transmission mechanism;and a heat eliminating means for absorbing a heat generated by the drivemotor through the use of cooling water supplied from a cooling watersource, to thereby prevent the heat from being transmitted from thedrive motor to the precision transmission mechanism;

wherein said heat eliminating means comprises:

a bracket means arranged between the precision transmission mechanismand the drive motor, and includes a first end in contact with an endsurface of the drive motor provided on a side at which an output shaftof the drive motor is arranged, a second end thereof in contact with theprecision transmission mechanism, and an annularly grooved fluid passagepermitting the cooling water to flow therethrough, to thereby exhibit acooling effect;

a fluid supply conduit line for providing a fluid connection between thecooling water source and the annular fluid passage of the bracket means,to thereby permit the cooling water to flow into the annular fluidpassage; and

a fluid return conduit line for providing a fluid connection between theannular fluid passage of the bracket means and the cooling water source,to thereby permit the cooling water to return from the annular fluidpassage to the cooling water source.

While the laser robot is in operation, the bracket means is forciblycooled by constantly circulating the cooling water through the fluidsupply circuit, the annular fluid passage of the bracket means and thefluid return circuit and the cooling water source essential to coolingthe laser beam conduit line system of the robot unit, and the bracketmeans arranged between the electric drive motor and the precisiontransmission mechanism absorbs heat generated by the electric drivemotor, to thereby prevent a transfer of the heat from the electric drivemotor to the precision transmission mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the ensuing description of thepreferred embodiment, taken in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is a front view, in part cross sectional, of an essential portionof a laser robot provided with a heat eliminating means in accordancewith the present invention;

FIG. 2 is a sectional view taken along the line II--II of FIG. 1;

FIG. 3 is a general side elevation of a laser robot provided with a heateliminating means in accordance with the present invention;

FIG. 4 is a rear end view taken in the direction of the arrows along theline IV--IV of FIG. 3; and

FIG. 5 is a graphical view comparatively, illustrating the heateliminating effect of the present invention and that of the prior art.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring first to FIGS. 3 and 4, a laser robot 10 is provided with arobot base 12, a robot swivel post 14 set upright on the robot base 12for turning about an longitudinal axis, an elongated, extendable robotarm 16 pivotally joined to the robot swivel post 14 for a up-and-downswing motion in the directions of the arrows V about a horizontal axisrelative to the robot swivel post 14, a robot wrist 18 joined to anextremity of the robot arm 16, and a laser beam projecting unit 20.

A laser beam to be projected by the laser beam projecting unit 20 is ledthrough suitable conduit lines from an external laser beam oscillator tothe robot unit. Then, as indicated by the arrows, the laser beam entersthe robot unit from above the robot swivel post 14, and is reflected bya laser beam reflecting mirror (not shown) provided on the axis of swingmotion of the robot arm 16 on the robot swivel post 14 to be deflectedto thereby travel through the robot arm 16. The laser beam is furtherdeflected in the robot arm 16 by a mirror (not shown), and then travelsalong the longitudinal axis of the robot arm 16 toward the robot wrist18. Within the robot wrist 18 is formed a laser beam conduit line havinga mirror, to again deflect the laser beam and direct it toward the laserbeam projecting unit 20, and to project the laser beam outside through acondensing lens system. The robot arm 16 of the laser robot 10 of thisembodiment has a bellows-like construction and is capable of extendingand contracting along its longitudinal axis. Therefore, the laser beamis guided by a telescopic laser beam conduit line provided within therobot arm 16.

As mentioned above, the laser robot 10 is internally provided with thelaser beam conduit lines and reflecting mirrors for reflecting the laserbeam. Since the reflecting mirrors that reflect the laser beam having ahigh energy are heated to a high temperature by the laser beam, thelaser robot 10, as well as the conventional laser robot, is providedwith a cooling water circulating circuit for supplying cooling waterfrom an external cooling water source through cooling water supply linesto the reflecting mirrors, to cool the same, and for returning thecooling water through cooling water return lines to the cooling watersource.

The laser robot 10 has a drive motor Mθ mounted on the robot base 12 onone side thereof to drive the robot swivel post 14 for turning about itslongitudinal axis. The drive motor Mθ drives the robot swivel post 14 toturn about the longitudinal axis thereof in opposite directions througha transmission mechanism (not shown) such as a belt-and-pulleymechanism.

A housing 24 is pivotally supported on a support bracket 22 laterallyprojecting from the substantially middle portion of the robot swivelpost 14. Enclosed by the housing 24 is a joint joining the output shaftof a drive motor Mv for driving the robot arm 16 for swing motion and aball screw shaft 30, i.e., a component of a transmission mechanism. Asuitable coupling means 66 (FIG. 1), such as an Oldham coupling, andbearings 64 (FIGS. 1 and 2) supporting the ball screw shaft 30 areenclosed by the housing 24. A bracket member 26 provided with an annularcooling water passage is interposed between the lower end of the housing24 and the end surface (the surface of the flange) of the drive motor Mvon the side of the output shaft of the same, and the drive motor Mv isfastened to the housing 24 with fastening means, such as bolts, tothereby hold the bracket member 26 between the housing 24 and the drivemotor Mv. The bracket member 26 is in close contact with the lowersurface of the housing 24, and is fastened to the housing 24 with bolts28 in a watertight fashion, which will be later described.

A screw nut 32 engaging the ball screw shaft 30 linearly moves along theaxis of the ball screw shaft 30 depending on a direction of rotation ofthe ball screw shaft 30 when rotated. Thus, the ball screw shaft 30 andthe nut 32 constitute a ball screw transmission mechanism. The linearmovement of the nut 32 of the ball screw transmission mechanism istransmitted to the robot arm 16 by a linkage 34 connected to the nut 32to swing the robot arm 16 either upward or downward about an axis C ofswing motion. Indicated at 36 in FIGS. 3 and 4 is a cable housingenclosing electric cables and flexible pipes for passing a coolingliquid for cooling the laser beam reflecting mirrors.

Referring to FIGS. 1 and 2 illustrating an essential portion of the heatabsorbing means incorporated into the laser robot 10 in an enlargedview, the bracket member 26 is provided with a cooling water passage 50in the shape of an annular groove, in a surface thereof contiguous withthe housing 24. The bracket member 26 is formed of a structuralmaterial, such as a metallic material, substantially in the shape of aring member, and an annular groove is formed in the upper surface of thering-shape bracket member 26. The annularly grooved upper surface of thebracket 26 is in close contact with the lower surface of the housing 24,and sealing members 52 such as 0-rings, are arranged between the uppersurface of the bracket member 26 and the lower surface of the housing 24to surround the annular groove to form the watertight cooling waterpassage 50. A lateral internally threaded cooling water inlet port 54aand a lateral internally threaded cooling water outlet port 54b areformed in the bracket member 26, and well known nipples or tube fittingsare screwed in the cooling water inlet port 54a and the cooling wateroutlet port 54b. A cooling water supply tube 56 and a cooling waterreturn tube 58 are connected to the nipples or the tube fittings to forma cooling water circulating circuit for circulating cooling waterthrough the annular cooling water passage 50. The cooling water supplytube 56 and the cooling water return tube 58 are bound together with anelectric cable 60 connected to the drive motor Mv with clamps, areextended through the robot swivel post 14 and are suitably connected toa cooling water supply system for the laser beam conduit lines to supplythe cooling water to and to return the cooling water from the annularcooling water passage 50.

Since the bracket member 26 provided with the annular cooling waterpassage 50 is inserted between the drive motor Mv and a precisiontransmission mechanism comprising the ball screw mechanism, the bracketmember 26 is constantly cooled by a forced cooling while the laser robot10 is in operation and, consequently, the heat generated by the drivemotor Mv is transferred by conduction from the flange of the drive motorMv to the bracket member 26 and is absorbed by the cooled bracket member26 to eliminate heat generated by the drive motor Mv, so that thetransmission of heat from the drive motor Mv to the housing 24 isintercepted by the bracket member 26. Namely, a heat flow from thehousing 24 through the components enclosed by the housing 24, such asthe bearings 64, to the ball screw shaft 30 is intercepted.

Thus, a heat transfer to the ball screw shaft 30 is prevented, tothereby remove the cause of a thermal deformation of the ball screwshaft 30. Namely, the bracket member 26 acts as a thermal insulator tothermally isolate the precision transmission mechanism including theball screw shaft 30 from the drive motor Mv. It should be noted that theflow rate of the cooling water to be circulated through the coolingwater passage 50 of the bracket member 26 need not be high, and may besuch a flow rate as capable of absorbing the heat transferred to thebracket member 26, because only a part of the heat generated by thedrive motor Mv that can be transferred by conduction through the bracketmember 26 and the housing 24 to the precision transmission mechanismneeds to be absorbed, and the bracket member 26 is not required toabsorb the rest of the heat dissipated around the drive motor Mv.Accordingly, the annular groove of the annular cooling water passage 50need not be large.

When removing the drive motor Mv and the ball screw shaft 30 forreplacement to carry out a maintenance service for the laser robot 10,the bracket member 26 may be kept fastened to the housing 24 with thebolts 28, and the 0 rings 52 thus maintain a watertight sealing.Therefore, there is no possibility that the cooling water will leak fromthe annular cooling water passage 50, and thus no additional effort needbe exerted to prevent the leakage of the cooling water, and themaintenance service can be simply achieved.

The laser robot in the foregoing embodiment is provided with the annularcooling water passage formed in the bracket member inserted between thetransmission mechanism and the drive motor for driving the robot arm,and according to the concept of the present invention, the drive motoris not cooled directly and the flow of heat to the transmissionmechanism, which is subject to a change in the operating accuracythereof due to thermal deformation, is intercepted by inserting a singlebracket member in the heat transfer path and forcibly cooling thebracket member by the cooling water for cooling the reflecting mirrorsfor deflecting the laser beam. Accordingly, it is to be understood thatthe present invention is applicable to various laser robots other thanthe laser robot in the described embodiment.

A graph shown in FIG. 5 proves that the precision transmission mechanismof the laser robot with the heat eliminating means in accordance withthe present invention reaches a thermal equilibrium in a very shorttime, compared with that of the laser robot of the prior art. As isobvious from FIG. 5, the precision transmission mechanism of the laserrobot of the present invention reaches a thermal equilibrium in a shorttime T₁, and the equilibrium temperature of the same is very low,whereas the precision transmission mechanism of the laser robot of theprior art requires a long time T₀, and the equilibrium temperature ofthe same is comparatively high.

As apparent from the foregoing description, the present inventionprevents a heat transfer by conduction to the precision transmissionmechanism of a laser robot, to thus enable the precision transmissionmechanism to be maintained at a high level of operating accuracy. Theheat eliminating means in accordance with the present invention avoids adirect heating from the electric motor, i.e., a component that generatesheat, and inserts the bracket member provided with the annular coolingwater passage for intercepting the flow of heat between the electricmotor and the precision transmission mechanism. Therefore, the heatelimination capacity of the bracket member required for a desired heateliminating effect can be smaller than that of a means for directlycooling the electric motor. Moreover, since the cooling water forcooling the laser beam reflecting mirrors of the laser robot is used asa cooling medium, the adverse effect of heat on the transmissionmechanism of an existing laser robot can be eliminated simply byincorporating the bracket member provided with the annular cooling waterpassage into the existing laser robot.

Still further, whereas cooling the driving motor for driving the robotarm with a cooling fan or the like unavoidably needs a large sizecooling unit, the heat eliminating means including the bracket memberprovided internally with the cooling means in accordance with thepresent invention has a compact construction and does not adverselyaffect the maintainability of the laser robot.

I claim:
 1. A laser robot comprising: a robot base, a robot swivel postarranged upright on the robot base to be turnable about a vertical axis;an axially extendable robot arm joined to the robot swivel post to beswingable up and down in a vertical plane relative to the robot swivelpost and provided with laser beam conduit lines formed therein to lead alaser beam toward an extreme end thereof; a laser beam projecting unitattached to the extreme end of the robot arm for projecting the laserbeam led thereto; a drive motor for driving a swing motion of the robotarm via a projection transmission mechanism; and a heat eliminatingmeans for absorbing a heat generated by the drive motor by the use of acooling water supplied from a cooling water source, to thereby preventthe heat from being transmitted from the drive motor to the precisiontransmission mechanism;wherein said heat eliminating means comprises:abracket means arranged between the precision transmission mechanism andthe drive motor, and including a first end in contact with an endsurface of the drive motor provided on a side where an output shaft ofthe drive motor is arranged, a second end thereof in contact with theprecision transmission mechanism, and an annularly grooved fluid passageforming a first portion of a cooling water supply circuit, said coolingwater supply circuit being disposed to receive said cooling water fromsaid cooling water supply source to apply a cooling effect to saidbracket means; a fluid supply conduit line for providing a fluidconnection between the cooling water source and the annular fluidpassage of the bracket means, thereby forming a second portion of saidcooling water supply circuit; and a fluid return conduit line forproviding a fluid connection between the annular fluid passage of thebracket means and the cooling water source, forming a third portion ofsaid cooling water supply circuit, to thereby permit the cooling waterto return from the annular fluid passage to the cooling water source. 2.A laser robot according to claim 1, wherein said bracket means havingsaid annular fluid passage comprises an annular member held between saiddrive motor and a housing- enclosing the precision transmissionmechanism, said annular member being provided with a cooling water inletport and a cooling water outlet port respectively at diametricallyopposite positions of said annular fluid passage.
 3. A laser robotaccording to claim 1, wherein said precision transmission mechanismcomprises a ball screw mechanism including a nut, and a linkageinterlocking the nut of the ball screw mechanism and said robot arm. 4.A laser robot according to claim 1, wherein said cooling water source isone commonly used for supplying a cooling water to cool said laser beamconduit lines of said robot arm.